You could run the Covid-19 PCR test to 400 cycles, and if Covid-19 wasn’t there in the original sample, it won’t appear in the reaction regardless of how many cycles you carry it out.
The misunderstanding of the PCR process is profound.
Think of it this way: You put a piece of paper on a copier and make a copy. You then copy the paper and its copy. Then you copy the paper and the three copies. Repeat 20-40 times.
If the original paper was blank, how many times do you need to copy it to get (for example) a meaningful paragraph? You might end up with copies with “noise” on them, but you won’t get a neatly printed paragraph no matter how many copies you make. You’ll only see a neatly printed paragraph on the copies if it existed on the original paper.
That’s how PCR works.